The present invention relates to a hydraulic screw tensioning device for the tightening and loosening of highly stressed screws or bolts, and includes a cylinder supported on a machine part that is to be clamped by a threaded bolt and a nut at least one piston that is guided in a sealed manner in the cylinder, is periodically supplied with pressure, and rests against a change sleeve threaded onto a threaded end of the threaded bolt, a pressure medium connection fitting on the screw tensioning device, and a rotary sleeve disposed in the cylinder and positively connected with the nut.
A screw tensioning device of this type is described in CH 552 448 A.
The object of such screw tensioning devices is to apply a precisely prescribed tensioning force onto a screw in order to be able to tighten or loosen the nut that is threaded onto the screw. For this purpose, the change sleeve in the screw tensioning device is threaded onto the projecting threaded end above the nut and thereafter the screw tensioning device is placed under hydraulic pressure. When the prescribed screw extension is achieved the nut that is threaded onto the threaded end of the threaded bolt is rotated along until it rests against the machine part.
To facilitate screwing-on of the change sleeve upon the threaded end of the threaded bolt with stationary screw tensioning cylinders, with the device of CH 552 448 A the pistons are provided at the top with a square or hexagonal extension. A turning tool, for example in the form of a manually operated “ratchet”, can be placed on the square or hexagonal extension, and the piston, with the housing stationary, can be rotated and hence threaded onto or off of the threaded end. After the threaded bolt is clamped with the desired force, the nut is adjusted, with the aid of a tool through an opening in the cylinder, until it again rests fully against the machine part.
The time for tightening such highly stressed screws is dependent very greatly upon the secondary times, i.e. the threading of the change sleeve onto the threaded end of the threaded bolt as well as the adjustment of the nut.
It is an object of the present invention to shorten the secondary times during the use of a hydraulic screw tensioning device as much as possible, whereby this is to be achieved with the aid of a device that has as straightforward a construction as possible.